Gastroblastoma mimics the embryonal mesenchyme of the foregut: A case report.

Background: Gastroblastoma is a rare gastric tumor composed of epithelial and spindle cell components. Identification of the characteristic MALAT–GLI1 fusion gene has only been reported in 5 cases. We report the morphological characterization of gastroblastoma with the MALAT1–GLI1 fusion gene in a young Japanese woman. Case presentation A 29-year-old Japanese woman visited Iwate Medical University Hospital with upper abdominal pain. Computed tomography revealed a tumor in the expansive lesions involving the gastric antrum. Histologically, we observed a biphasic morphology composed of epithelial and spindle cell components. The epithelial components appeared as slit-like glandular structures and tubular or rosette-like differentiation. The spindle cell components consisted of short spindle-shaped oval cells. Immunohistochemical (IHC) analysis revealed that the spindle cell component was positive for vimentin, CD10, CD56, GLI1, HDAC2 and focally positive for PD-L1. The epithelial component was positive for CK AE1AE3, CAM5.2, CK7, and negative for CK20 and EMA. Both components were negative for KIT, CD34, DOG1, SMA, desmin, S100 protein, chromogranin A, synaptophysin, CDX2, and SS18-SSX. Finally, MALAT-GLI1 fusion gene was molecularly detected. Conclusions We report the following new findings with this case: (i) gastric tumors mimic the gastrointestinal mesenchyme in the embryonic period; (ii) nuclear expression of PD-L1 and HDAC2 were observed in the spindle cell component of gastroblastoma. We speculate that HDAC (Histone Deacetylase) inhibitors may offer a promising treatment option for gastroblastoma.